The production of silanes, whether halosilane or organohalosilane or organohalohydrosilane, has long been known. The organohalohydrosilanes have found many applications and are generally useful intermediates for the synthesis of organosilicon coupling agents, silicone surfactants and in hydrosilylation and redistribution reactions. In fact, these compounds have come into such demand that the supply of the organohalohydrosilanes obtainable by current processes often does not satisfy the demand.
The direct reaction process described in U.S. Pat. No. 2,380,995, issued to Rochow, discloses the reaction of silicon with a methylhalide in the presence of a catalyst. This process, however, produces a mixture of silicon products with the methylhalohydrosilanes being produced in low yield and constituting only a small amount of the mixture, generally less than about 5 wt. % CH.sub.3 SiHCl.sub.2 and less than about 1 wt. % of (CH.sub.3).sub.2 SiHCl with no CH.sub.3 SiH.sub.2 Cl when the methylhalide is mechylchloride. The bulk of the products produced consisted of HSiCl.sub.3, SiCl.sub.4, (CH.sub.3).sub.3 SiCl, CH.sub.3 SiCl.sub.3, (CH.sub.3).sub.2 SiCl.sub.2 and disilanes of the structure (CH.sub.3).sub.x Si.sub.2 Cl.sub.6-x, as well as a number of disilamethanes, siloxanes and hydrocarbons as shown in U.S. Pat. Nos. 2,598,435, 2,681,355, and 2,709,176. These mixtures require complex distillation processes to isolate and purify the small quantities of methylchlorohydrosilanes produced from hydrocarbon by-products of similar boiling points, as can be seen in U.S. Pat. No. 3,704,260 issued Nov. 28, 1972 to M. J. Wynn, and U.S. Pat. No. 4,181,673 issued Jan. 1, 1980 to H. Schumann, et al.
Voorhoeve (Organohalosilanes: Precursors to Silicones, Elsevier, N.Y., 1967, pp. 190-201) reports C.sub.2 H.sub.5 SiHCl.sub.2 as the principal product of the direct reaction of ethyl chloride with copper-activated silicon. The more desirable C.sub.2 H.sub.5).sub.2 SiHCl and C.sub.2 H.sub.5 SiH.sub.2 Cl are reportedly not obtained even when hydrogen is added along with the ethyl chloride at pressurized reaction conditions, as further shown in German Offen. No. 859,164, published Dec. 11, 1952 and Turetskaya, et al., Khim. Prom., p 18 (1963). These procedures fail to produce all three of the desired organohalohydrosilanes at a satisfactory high rate and/or selectivity.
Though various methods for the preparation of silanes using hydrogen, hydrogen chloride or metal hydrides have been published, they have all failed to satisfy the burgeoning demand for organohalohydrosilanes. Catalytic hydrogenation processes for the synthesis of (CH.sub.3).sub.2 SiHCl and CH.sub.3 SiHCl.sub.2 from methylchlorodisilanes are disclosed in U.S. Pat. No. 3,639,105, issued Feb. 1, 1972 to W. H. Atwell, et al., U.S. Pat. No. 4,059,608, issued Nov. 22, 1977 to Calas, et al. and U.S. Pat. No. 4,079,071, issued Mar. 14, 1978 to R. S. Neale. These processes require use of the disilanes as a starting material, however, the disilanes represent only a small fraction of the product usually obtained in a direct reaction process. For instance, in U.S. Pat. No. 4,500,724, issued Feb. 19, 1985 to Ward, et al., the disilanes represent from about 1 to 6 wt. % of the silanes produced. Further, the disilanes produced are typically deficient in [Cl(CH.sub.3).sub.2 Si].sub.2, which leads to high yields of (CH.sub.3).sub.2 SiHCl. The hydrochlorination of disilanes, as disclosed in U.S. Pat. Nos. 2,709,176, loc. cit., 2,842,580, and in Calas, et al., J. Organomet. Chem, 225, 117-130 (1982) typically results in more CH.sub.3 SiCl.sub.3, CH.sub. 3 SiHCl.sub.2 and (CH.sub.3).sub.2 SiCl.sub.2 and no (CH.sub.3).sub.2 SiHCl or CH.sub.3 SiH.sub.2 Cl.
Attempts at direct hydrogenation of alkylhalosilanes to alkylhalohydrosilanes have also been unsuccessful. The reaction is slow even at temperatures as high as about 1000.degree. C. and pressures of about 1500 psig using Pd catalysts (Japanese Patent No. 82-47917; U.S. Pat. No. 2,595,620). This reaction introduces a further complication since the organohalodyrosilanes of the formulas R.sub.2 SiHCl and RSiH.sub.2 Cl are not sufficiently stable to withstand such high temperatures.
Syntheses of alkylchlorohydrosilanes via the metal hydride reduction of alkylchlorosilanes with NaH, Chalk, J. Organomet. Chem., Vol. 21, 95-101 (1970); Antipin et al., Russ. J. Gen. Chem., Vol. 40, p. 789 (1970); U.S. Pat. No. 3,704,261 issued Nov. 28, 1972 to Berger, et al.; CaH.sub.2 (Simon, et al., J. Organomet, Chem., Vol. 206, p. 279 (1981)), NaBH.sub.4 (U.S. Pat. No. 4,115,426 issued Sept. 19, 1978 to Hillrod, et al.) and LiAlH.sub.4 (Eaborn, et al., J. Organomet. Chem., Vol. 18, p. 371 (1969)) are also disclosed. These are not practiced commercially because of the relatively high cost of metal hydrides and the need to dispose of the stoichiometric amounts of metal chlorides that are formed during the reduction reactions.
The yield of organohalohydrosilanes of formula RHSiX.sub.2 is increased by the use of organochloride (e.g. CH.sub.3 Cl) and hydrogen halide (e.g. HCl) mixtures in the Rochow direct reaction synthesis (see Gorbunow, et al., Dokl. Akad. Nauk. SSR., Vol. 194, p. 92 (1970)). However, large quantities of the much less desirable RSiX.sub.3 are simultaneously formed and the method is uneconomic.
The use of hydrogen-organohalide (e.g. CH.sub.3 Cl, C.sub.2 H.sub.5 Cl) mixtures in the Rochow direct reaction synthesis is disclosed in the following references: U.S. Pat. No. 2,380,998 issued Aug. 7, 1945, issued to Sprung, et al.; Brit. Pat. Nos. 590,654; 575,674; Ger. Pat. No. 859,164; Turetskaya et al., Khim. Prom., p. 18 (1963). These disclosures report increased formation of RHSiCl.sub.2, but not R.sub.2 SiHCl or RSiH.sub.2 Cl.
DeCooker, et al., (J. Organomet. Chem., Vol. 99, p. 371 (1975); Ph.D. Diss. Univ. Delft, The Netherlands, 1976, Chps. 5 and 6) disclose that the addition of Zn, Cd, and Al to the copper-activated silicon used in the direct reaction synthesis with mixtures of CH.sub.3 Cl and H.sub.2 at 300.degree. C.-370.degree. C. lowers the selectivity to CH.sub.3 SiHCl.sub.2 and (CH.sub.3).sub.2 SiHCl. A summary of their results is shown in Table 1. The data show that selectivity to the methylchlorohydrosilanes is favored by high hydrogen partial pressures and high temperatures. However, the reaction rates are low and erratic and stable contact mass activity is not attained (DeCooker, 1976, Ph.D. Diss., Chp. 5, pp. 57-63; Chp. 6, pp. 64-73) even with the use of 10-15 wt. % Cu catalyst. Additionally, reaction performance parameters such as the ratio of CH.sub.3 SiHCl.sub.2 to (CH.sub.3).sub.2 SiHCl and the overall preference of the methylchlorohydrosilanes (i.e., CH.sub.3 SiHCl.sub.2 +(CH.sub.3).sub.2 SiHCl) are variable even for duplicate experiments. The dissertation presents kinetics data (Chp. 6) on the direct reaction synthesis of CH.sub.3 SiHCl.sub.2 and (CH.sub.3).sub.2 SiHCl from a contact mass (i.e., intimate mixture of Si, Cu, and Cu alloyed with Si) containing 0.1 wt. % Zn and 0.05 wt. % f Al. However, the maximum tolerable levels of Zn, Cd, and Al conducive to high selectivity to the desired compounds and stable mass activity are not defined. It is noteworthy (Chp. 6, p. 64) that the authors associate low selectivity to the methylchlorohydrosilanes with low CuCl concentrations. There are no teachings with respect to operation at superatmospheric pressures.
TABLE 1 __________________________________________________________________________ Direct Synthesis of CH.sub.3 SiHCl.sub.2 and (CH.sub.3).sub.2 SiHCl According to DeCooker* Rate H.sub.2 Partial Si Conv., Temp. Cu Zn Al DM MD T D gm CH.sub.3 Cl/ Press. (atom) wt. % .degree.C. wt. % wt. % wt. % mole % mole % mole % mole % kg Si, Hr __________________________________________________________________________ 0.55 20 332 10 -- -- 32.7 37.6 3.4 23.4 75 0.55 40 332 10 -- -- 30.8 23.8 9.9 33.1 100 0.75 55 332 10 -- -- 33.1 45.7 6.9 12.5 75 0.55 65 332 10 -- -- 24.4 51.1 4.8 17.3 85 0.55 25 332 10 0.1 0.05 17.5 30.8 4.7 45.8 40 0.75 50 332 10 0.1 0.05 28.5 56.7 2.7 10.3 40 0.75 60 332 10 0.1 0.05 17.5 70.3 2.7 5.0 50 0.58 20 370 10 0.1 0.05 23.0 26.6 5.3 42.1 180 0.58 50 370 10 0.1 0.05 31.6 39.5 3.2 23.9 290 0.55 20 334 15 0.1 0.05 13.4 29.5 3.2 49.5 65 0.55 40 334 15 0.1 0.05 17.4 36.0 4.1 39.6 75 0.55 70 334 15 0.1 0.05 8.0 62.4 12.7 5.4 50 __________________________________________________________________________ *Data from Ph. D. Dissertation, Univ. Delft (1976). Chp. 5 and 6. DM = (CH.sub.3).sub.2 SiHCl, MD = CH.sub.3 SiHCl.sub.2, T = CH.sub.3 SiCl.sub.3, D = (CH.sub.3).sub.2 SiCl.sub.2.
French Patent No. 1,523,912 discloses the direct reaction synthesis of CH.sub.3 SiHCl.sub.2 and (CH.sub.3).sub.2 SiHCl with CH.sub.3 Cl--H.sub.2 mixtures at 350.degree. C.-380.degree. C. and 0-2.5 atmospheres gauge in which selectivity to the methylchlorohydrosilanes is improved by the addition of salts of the Group VIII metals (e.g., chlorides, oxalates and formates of Fe, Co, Ni) at 0.3-10 wt. %, preferably 0.3-2 wt. %, of the silicon contact mass. The formation of (CH.sub.3).sub.2 SiHCl and CH.sub.3 SiHCl.sub.2 under the conditions illustrated in the examples of the patent is shown in Table 2.
Contrary to the teachings of DeCooker (loc. cit.) this French patent discloses (Examples 5 and 8; Claim 6) that 0.25-0.5 wt. % ZnCl.sub.2 (equivalent to 0.12-0.25 wt. % Zn) is advantageously included in the mass to improve selectivity to the methylchlorohydrosilanes. However, there are no teachings regarding the control of the ratio of CH.sub.3 SiHCl.sub.2 to (CH.sub.3).sub.2 SiHCl, or of the useful range of hydrogen partial pressures or of the maximum tolerable levels of other metals such as Cd, Al, or Sn. Examples 8 employs 15 wt. % Cu, but the useful copper catalyst levels are not otherwise defined. The reaction performance in the absence of the Group VIII metal salts is also not reported. Additionally, the conduct of the synthesis at 2.5 atmospheres gauge and 350.degree. C. with 2.5 wt. % NiCl.sub.2 as additive destroys the selectivity to (CH.sub.3).sub.2 SiHCl (compare examples 1 and 3 of Table 2).
TABLE 2 __________________________________________________________________________ Direct Synthesis of (CH.sub.3).sub.2 SiHCl and CH.sub.3 SiHCl.sub.2 According to Fr. Pat. 1,523,912 H.sub.2 DM MD T D Rate Additive Example Vol. % Wt. % Wt. % Wt. % Wt. % gm/kg Si, Hr MD/DM D/T __________________________________________________________________________ 2.5 wt. % NiCl.sub.2 1 35.7 8.0 27.3 20.8 40.4 149 3.41 1.94 2.5 wt. % CoCl.sub.2 2 7.1 4.0 37.0 33.0 22.5 75 9.25 0.68 2 wt. % Ni(C.sub.2 O.sub.4) 4 35.7 7.0 27.0 26.7 37.2 128.5 3.86 1.39 2 wt. % Co(C.sub.2 O.sub.4) 6 35.7 8.8 30.8 17.6 36.8 97.6 3.5 2.09 2 wt. % Fe(C.sub.2 O.sub.4) + 5 35.7 15.5 32.9 13.2 34.2 145.8 2.12 2.59 0.25 wt. % ZnCl.sub.2 2 wt. % Fe(HCOO).sub.2 + 8 35.7 6.3 52.1 17.9 17.2 8.6 8.27 0.96 0.5 wt. % ZnCl.sub.2 2 wt. % NiCl.sub.2 3 27.3 -- 42.9 25.1 19.1 164 -- 0.76 __________________________________________________________________________ All experiments at 380.degree. C., 0 atom. gauge except Example 3, which was run at 350.degree. C., 2.5 atom. gauge. DM = (CH.sub.3).sub.2 SiHCl, MD = CH.sub.3 SiHCl.sub.2, T = CH.sub.3 SiCl.sub.3, D = (CH.sub.3).sub.2 SiCl.sub.2.
As is shown, the literature fails to disclose a suitable direct reaction process capable of satisfying the demand for organohalohydrosilanes. None of the references disclose or suggest process conditions leading to the stable, reproducible formation of organohalohydrosilanes, in particular, alkylchlorohydrosilanes, that yield both high reaction rates and high selectivity to organohalohydrosilanes with good reproducibility and process stability.